RCD Snubber Introduction & Designing

In previous post we discussed Switching losses in the Resistive Loads, in this post we will discuss problems in Inductive Load and also aid to reduce the Losses in Inductive Loads, there are many way to reduce the Losses in inductive loads but we will only discuss RCD Snubber and its Designing here.

First lets discuss about how inductive Loads behave when it is used in switching Circuits, as you can see this in below figure, when device is turning off Voltage is rising quickly as compared to Resistive load.

Now we will not go to detail of how we calculated the Woff and Won , below are the given formulas for calculating Switching Losses for Inductive Loads

Switching Loss for turning off profile

Switching Loss for inductive load in turning ON profile

Comparison of Resisitive and Inductive Load:

Comparison of Resistive Loads vs Inductive Load

Now as you can see as compared to the Resistive Load Inductive switching loss value will be more.

How to Reduce the Inductive Load Switching Loss:

Inductive Switching loss can be decreased by RCD Snubber aid, As you can see in following diagram that by addition of RCD snubber circuit, the voltage of rise across the switching device is delayed hence decreaing the area under the curve is decreased therefore the switching loss across the device is decreased

How does RCD Snubber Circuit Works?

As you can see in above picture when device is turned off, inductor was already charged and then RCD snubber circuit comes into play, Inductor discharges through Diode and Capacitor in RCD snubber circuit, now device is ready to Turn ON again. This cycle continues for all turn off profiles, inductor has to be fully discharged every time before turning ON. In this way losses from inherent voltage spikes of the Inductor will be reduced.

Important Formulas to Design RCD Snubber?

Pd=